The present invention relates to a bootstrap type output circuit composed of field effect transistors.
Bootstrap type output circuits (bootstrap circuits) have been widely utilized in various fields because the circuits can produce signals at the level of a power supply voltage without any level reduction. Bootstrap circuits generally consist of an output (buffer) section, including an output transistor connected between an output terminal and a power voltage terminal with a bootstrap capacitor coupled to the gate of the output transistor, and a delay control section for controlling charging operation of the capacitor in response to an input signal. The delay control section provides an output signal to initiate the charging operation of the capacitor a predetermined period after the input signal changes from a first low level to a second high level. After the predetermined period, the charge stored in the capacitor is superimposed on the gate potential of the output transistor so that the output transistor is driven into the saturated region to generate the power voltage level at the output terminal.
In the conventional circuit, the delay control section is kept at a high impedance state and is likely to be affected by noise from the outside, fluctuation of a substrate biasing voltage, or the like. In that case, it becomes difficult to effectively charge the capacitor, thereby adversely affecting the operation of the output circuit.